The present invention relates to a rolling bearing unit with a rotational speed sensor which is used to rotatably support an automobile wheel to a suspension while detecting the rotational speed of the automobile wheel.
The rotational speed of the automobile wheel must be detected to control the antilock brake system (ABS) and traction control system (TCS).
FIGS. 1 and 2 show an example of the conventional structures of the rolling bearing unit with the rotational speed sensor, disclosed in JP Utility Model Publication JITSUKAI HEI NO. 7-31539 for such a purpose.
The rolling bearing unit with the rotational speed sensor has a stationary ring or outer ring 1 which does not rotate during use, and a rotating ring comprises a hub 2 which is rotatable during use and rotatably supported on the inner diameter side of the outer ring 1. An encoder 3 is fixed to part of the hub 2, and a sensor 4 is supported by the outer ring 1 to detect the rotational speed of the encoder 3.
Specifically, the outer ring 1 has an inner peripheral surface formed with outer ring raceways 5 in double rows. The rotating ring comprises, in addition to the hub 2, an inner ring 7 which is fitted onto the hub 2 and securely fixed to the hub 2 with a nut 6. The hub 2 and inner ring 7 have an outer peripheral surface formed with inner ring raceways 8. A plurality of rolling members 9 are rotatably provided between the outer ring raceways 5 and the inner ring raceways 8 and supported by cages 10, thereby rotatably supporting the hub 2 and inner ring 7 in the outer ring 1.
The hub 2 has an axially outer end portion which projects axially outward from the axially outer end of the outer ring 1 and has a flange 11 for mounting the automobile wheel thereto. The outer ring 1 has an axially inner end portion which is formed with a mount portion 12 for mounting the outer ring 1 to the suspension.
The term "axially outer" means the widthwise outside in the state of installation into the automobile, right in FIG. 1, and the term "axially inner" means the widthwise central side in the state of installation into the automobile, left in FIG. 1.
The gap between the opening portion at the axially outer end of the outer ring 1 and the outer peripheral surface at the middle portion of the hub 2 is closed off by a seal ring 13.
In the case of the rolling bearing unit for heavy automobiles, tapered rollers can be used instead of the balls illustrated for the rolling members 9.
The encoder 3 is fitted onto the outer peripheral surface of the inner ring 7 at an axially inner end portion separated from the inner ring raceway 8 to assemble the rotational speed sensor in the rolling bearing unit.
The encoder 3 is made of a magnetic metal plate such as carbon steel and formed generally in an annular shape with a L-shaped cross section by way of a plastic working process to comprise a cylindrical portion 15 and a circular ring portion 16. The cylindrical portion 15 is fitted and fixed to the axially inner end portion of the inner ring 7 with interference fit.
A number of through holes 17 are formed in the circular ring portion 16 to extend radially in a slit shape, and each being long in the diametrical direction of the circular ring portion 16, and arranged with a uniform interval in the circumferential direction, so that the magnetic characteristics of the circular ring portion 16 are changed circumferentially alternately with a uniform interval.
Fittingly fixed to the opening portion at the axially inner end of the outer ring 1 is a cover 18 which faces the axially inner surface of the circular ring portion of the encoder 3 to close off the opening at the axially inner end of the outer ring 1. The cover 18 is formed with a metal plate through a plastic working process and comprises a cylindrical fitting portion 19 fittingly fixed to the opening portion at the axially inner end of the outer ring 1 and a shield plate portion 20 to close off this opening. The shield plate portion 20 has a central portion formed with a bulge portion 21 in a bottomed cylindrical shape to prevent any interference between the shield plate portion 20 and the nut 6, and an outer peripheral portion formed with a through hole 22 located radially outward than the bulge portion 21 through which the detecting portion 24 of the sensor 4 is inserted into the inside of the cover 18.
A mount flange 25 is fixed to the outer peripheral surface at the middle portion of the sensor 4, and by fixing the flange 25 to the shield plate portion 20 of the cover 18 with stop screws 26, the sensor 4 is securely connected to the cover 18 in a predetermined position relation. In the state where the sensor 4 is fixed to the cover 18, the tip end of the detecting portion 24 faces the axially inner surface of the circular ring portion 16 through a minute clearance.
During use of the rolling bearing unit with rotational speed sensor as mentioned above, the mount portion 12 provided on the outer peripheral surface of the outer ring 1 is fixedly connected to the suspension with bolts (not shown), and the vehicle wheel is fixed to the flange 11 formed on the outer peripheral surface of the hub 2 with the studs 27 through the flange 11, thereby rotatably supporting the vehicle wheel to the suspension.
As the vehicle wheel rotates in this state, the through holes 17 in the circular ring portion 16 and the column portions between the circumferentially adjacent through holes 17 alternately pass by the end faces of the detecting portions 24 of the sensor 4. As a result, the density of magnetic flux through the sensor 4 changes and the output of the sensor 4 changes. The frequency at which the output of the sensor 4 changes, is proportional to the rotational speed of the vehicle wheel. Accordingly, the output of the sensor 4 is sent to the control devices (not shown), so as to control the ABS and TCS.
In the case of the conventional structures as shown in FIGS. 1 and 2, the sensor 4 is securely connected to the cover 18 with the screws 26 to reduce the man power for repair and replacement of the sensor. Specifically, bolts 28 are inserted into the through hole 54 in the mount flange 25 and into the through hole 56 in the cover 18 with the sensor 4 secured thereto, and the nuts 29 are threaded and tightened to the bolts 28, so that the sensor 4 is fixedly connected to the cover 18. When removing the sensor 4 from the cover 18, the nuts 29 are loosened and the sensor 4 is disengaged from the cover 18.
In the conventional structures of FIGS. 1 and 2, where the through holes 54, 56 are provided to be inserted by the bolts 28, any foreign matter such as dirty water may enter the space 30, where the rolling members 9 exist, from outside through the minute clearance around the bolts 28 inserted into the through holes 54, 56, which may result in that any corrosion and abrasion may be caused in the rolling members 9 and in the outer and inner ring raceways 5, 8, worsening the durability of the rolling bearing unit. In addition, the foreign matter such as magnetic powders adhere to the sensor 4 and encoder 16 to worsen the precision in detecting the rotational speed.
In addition, in the conventional structure, the operation to securely connect the sensor 4 to the cover 18 with screws is inconvenient and troublesome. Specifically, when the sensor 4 is fixed to the cover 18, the nuts 29 are threaded to the bolts 28 inserted to the through hole 54 in the mount flange 25 and to the through hole 56 in the cover 18, and then the bolts 28 and nuts 29 are tightened using a pair of tools such as spanner or wrench from the opposite sides of the cover 18.
Particularly, when installing the sensor 4 after the cover 18 is connected to the outer ring 1, the heads of the bolts 28 existing in the cover 28 could not be retained, and the process for clamping the bolts 28 and the nuts 29 must be done while the cover 18 is removed from the outer ring 1. Such a process to incorporate the sensor 4 is troublesome and inconvenient, which may cause the cost of the rolling bearing unit increased.